T2K ended its 2019-2020 data-taking run on February 12, 2020, with a record beam power of 515 kW stably delivered by the J-PARC Main Ring accelerator. T2K has accumulated a total of 3.64×10^21 protons on target (POT) so far.
The protons are produced by the J-PARC Main Ring synchrotron accelerator in Tokai on the east coast of Japan. The 30 GeV protons are directed onto a graphite target, producing charged pions and other secondary particles. These pions pass through three magnetic “horns,” which are able to preferentially focus either positively-charged or negatively-charged pions in the direction of T2K’s neutrino detectors. Positively charged pions quickly decay to produce muon neutrinos, while negatively charged pions decay to produce muon antineutrinos. This allows T2K to produce a beam composed mostly of muon neutrinos or muon antineutrinos by changing the direction of the magnetic horn current.
